1. Field of the Invention
The present specification generally relates to a sheet feeding device, feeding sheets one by one, an image forming apparatus including such a sheet feeding device, and, in particular, to a sheet feeding device and image forming apparatus capable of suppressing successive sheet jam occurable when a sheet feeding tray is detached and set.
2. Discussion of Related Art
A sheet feeding device is a well known device used in an image forming apparatus, such as a copier, a printer, a facsimile, an image scanner, a combined machine combining these apparatuses, etc., in order to feed printing sheets and original documents or the like one by one. Such a well known sheet feeding device generally includes a pickup roller 2C that contacts and feeds the topmost sheet P stacked on a sheet feeding tray 1c in a direction as shown by the arrow AC in FIG. 9 when rotating. Also included therein are a feed roller 3c and a reverse roller 4c contacting the feeding roller 3c both arranged downstream of the pickup roller 2c in a sheet conveyance direction. Such a feed roller 3c is connected and driven by a driving motor (not shown) via a feed clutch (not shown) in the sheet feeding direction as shown by the arrow BC. The reverse roller 4c is connected, via a torque limiter (not shown), to a reverse shaft 5c driven by the driving motor. The rotational direction of each of the rollers 2c, 3c, and 4c will be referred to as “a sheet feeding direction” when each rotates and feeds a sheet P downstream, and “a counter sheet feeding direction” when each reversely rotates and feeds the sheet upstream.
When only a sheet P1 is fed in a nip formed between the feed roller 3c and reverse roller 4c, the reverse roller 4c is engaged and driven by the moving sheet P in the sheet feeding direction as shown by the arrow CC due to a function of the torque limiter. When the next sheet P2 is fed in the nip together with the sheet P1, rotation of the reverse shaft 5c is transmitted to the reverse roller 4c via the torque limiter, causing the reverse roller 4c to rotate in the counter sheet feeding direction as shown by the arrow IC. As a result, the reverse roller 4c returns the next sheet P2 in the counter sheet feeding direction as shown by the arrow DC.
The above-mentioned sheet feeding device prevents double-sheet feeding, and is generally referred to as an FRR-type device. In such a known sheet feeding device, the next sheet P2 is stopped and pinched between these feed and reverse rollers 3c and 4c as shown in FIG. 10 after the last sheet has been launched in a series of sheet feeding operations. In such a situation, if a sheet feeding tray 1c is withdrawn in a direction perpendicular to the surface of FIG. 10, for example, an external force is applied to sheet P2, possibly causing successive sheet jam when the sheet feeding tray P2 is set again, because the sheet P2 remains pinched therebetween throughout the operation.
Various sheet feeding devices resolving such a problem have been historically proposed as given infra. However, these devices are complex, have a significantly high cost, and require a large number of component parts. For example, a sheet feeding device discussed in Japanese Patent Application Laid Open No. 10-218403 necessarily includes a reverse clutch to either connect or disconnect a reverse shaft from a reverse roller, thus increasing the cost of the entire apparatus.